Without limiting the scope of the invention, its background is described in connection with spinal joint prosthesis. A variety of artificial prosthesis are used to replace chronically injured or ruptured intervertebral discs and range from plate inserts, ball and socket joints, gel filled enclosures, spring-biased plates, plate and joint combinations and others.
For example, U.S. Pat. No. 6,846,328, issued to Cauthen teaches another articulating spinal implant. The articulating intervertebral disc replacement implant is formed from two elements, each engaging one of an adjacent pair of vertebra and capable of an articulating motion that resists compression and lateral movement between the vertebra, but allows the adjacent vertebra to articulate about an instantaneous axis of rotation.
Another example is taught in U.S. Pat. No. 6,039,763, discloses articulating spinal disc prosthesis that is designed to articulate in a manner resembling a human knee articulation. Briefly, the artificial spinal disc includes two plates each having a planar outer surface and an articulating inner surface. The planar outer surfaces contact and are affixed to adjacent inferior and superior surfaces of two adjacent vertebra. The interior articulating surfaces of the artificial spinal disc are shaped generally to have one or more complementary convex/concave shaped articulating portions that are shaped and articulate in a manner similar to a human knee.
Another example of intervertebral disc prosthesis is taught in U.S. Pat. No. 5,401,269, which discloses an intervertebral disc endoprosthesis that includes two prosthesis plates that have a prosthesis core that cooperates with at least one prosthesis plate via an articulating surface permitting a rotational movement. The two plates are connected to the end plates of adjacent vertebrae. To control rotational movement around the vertical axis, the articulating surface forms curved arches of different average radius in the median section and in the frontal section. The radius of curvature in the sagittal section is less than in the frontal section.